Demand for lower freight transportation cost is driving up the average freight car weight around the world. To carry heavier weight, the freight cars must be equipped with strong bearings capable of carrying both axial and radial loads. At the same time, the freight industry is pushed to carry heavier weights at higher speeds and with improved fuel efficiency.
Tapered roller bearings efficiently carry both axial and radial loads. A tapered roller bearing includes one or more rows of tapered rollers. Each row encircles the rotation axis of the bearing. Each tapered roller has the shape of a truncated cone. This geometry allows the tapered roller bearing to support axial loads (loads parallel to the rotation axis of the bearing). A popular choice for freight cars is the double-row tapered roller bearing which has two rows of tapered rollers. The two rows are tapered in opposite directions to locate the shaft, or journal, in both directions along the rotation axis.
Tapered roller bearings, as well as other types of roller bearings, operate with a lubricant within the bearing to reduce friction between the rollers and the raceways on which the rollers roll. To contain the lubricant within the bearing and to prevent water, dirt, and other contaminants from entering the bearing, the bearing is equipped with a seal. The seal may be a contact seal that forms a physical barrier between the inside of the bearing and the external environment. This physical barrier, however, requires direct contact between parts moving relative to each other, such as direct contact between one part that does not rotate and another part that rotates because it is affixed to a rotating journal. Thus, a contact seal is associated with friction which causes wear and tear of the components. Not only does the wear and tear result in damage and present a maintenance problem, but the friction also reduces fuel efficiency and may generate excessive heat at high speeds. In contrast, a noncontact seal has no direct physical contact between non-rotating and rotating parts (or between parts rotating at different speeds). One type of noncontact seal is a labyrinth seal, which forms a labyrinth between stationary and rotating parts (or between parts rotating at different speeds). The labyrinth seal limits transport of material between the interior of the bearing and the external environment to a tortuous path that reduces or prevents both loss of lubricant from the bearing and entry of contaminants into the bearing. Some labyrinth seals include a slinger that rotates with the journal. The slinger's rotation, especially when operating at high rotation speeds, further prevents both transport of lubricant out of the bearing and entry of contaminants into the bearing. Labyrinth seals are not restricted to noncontact seals but may also include a resilient gasket to form a contact seal with minimal friction.